Axial expandable exhaust duct

ABSTRACT

An exhaust duct for an engine includes an outer exhaust duct and a nested exhaust duct capable of having at least two configurations. The nested exhaust duct is circumferentially surrounded by the outer exhaust duct for a first length of the nested exhaust duct in a first configuration. The nested exhaust duct is circumferentially surrounded by the outer exhaust duct for a second length of the nested exhaust duct in a second configuration, which is less than the first length.

BACKGROUND

The present disclosure relates generally to attritable aircraft engines.More specifically, this disclosure relates to manufacturing of anexpandable exhaust duct for an attritable aircraft engine.

Attritable aircraft can include, for example, Unpiloted (or Unmanned)Aerial Vehicles (UAVs) and expendable turbojet systems for guidedmunitions, missiles, and decoys. Attritable aircraft are generallydesigned as a limited lifetime vehicle, which can be as short as asingle use or single mission vehicle. As such, many components andfeatures common in traditional piloted aircraft are unnecessary or canbe simplified for attritable aircraft applications.

For example, an exhaust duct of a traditional aircraft engine can addsignificant axial length to the engine. Generally, the larger the enginebeing manufactured the larger the tooling equipment needed formanufacture, increasing the cost of the tooling. Additionally, largerengines can be more expensive to ship from the site of manufacture to anend user. There exist needs in various industries to reduce the size ofmanufactured parts, thereby reducing manufacturing costs and simplifyingpackaging.

SUMMARY

An exhaust duct for an engine includes an outer exhaust duct and anested exhaust duct capable of having at least two configurations. Thenested exhaust duct is circumferentially surrounded by the outer exhaustduct for a first length of the nested exhaust duct in a firstconfiguration. The nested exhaust duct is circumferentially surroundedby the outer exhaust duct for a second length of the nested exhaust ductin a second configuration, which is less than the first length.

A method of manufacturing an axially extendable exhaust duct for anengine includes manufacturing an outer exhaust duct and a nested exhaustduct capable of having at least two configurations. The nested exhaustduct is circumferentially surrounded by the outer exhaust duct for afirst length of the nested exhaust duct in a first configuration. Thenested exhaust duct is circumferentially surrounded by the outer exhaustduct for a second length of the nested exhaust duct in a secondconfiguration, which is less than the first length.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross-sectional views of an exhaust duct for anattritable engine in a nested and an expanded state, respectively.

FIGS. 2A and 2B are perspective views of the inner section of theexhaust duct showing springs in an uncompressed and a compressed state,respectively.

FIG. 3A is a perspective view of one embodiment of the spring.

FIG. 3B is a perspective view of one embodiment of the spring.

FIG. 4A is a perspective view of the nested exhaust duct including theuncompressed spring.

FIG. 4B is a perspective view of the outer exhaust duct including thekey.

FIG. 4C is a perspective view of the expanded exhaust duct positioned inan extended state inside the outer exhaust duct.

FIG. 5 is a cross-sectional view of the nested exhaust duct in anextended state including the compressed spring.

DETAILED DESCRIPTION

An attritable engine with an integrally built extendable exhaust duct isdisclosed herein. The attritable engine leverages additive manufacturingtechniques to improve various aspects of the limited-life engine. Forexample, additive manufacturing allows the assembly details to beunitized and, simultaneously permits integration of many complexperformance-enhancing features. The additively manufactured enginereduces the time to delivery to the customer and lowers the overallproduction costs of the unit.

An attritable engine with an integrally built extendable exhaust ductcan be assembled into place without any secondary operations, whichdecouples the axial length of the design build from the size of thebuild chamber. The extendable exhaust duct can be pulled axially awayfrom the inlet side of the unitized body and locked into place after thebuild process is complete. Reducing the axial length of the attritableengine during manufacture, decreases the overall build time, reducingcosts. Furthermore, the attritable engine prior to extending the exhaustduct has a smaller footprint and, as such, is easier and less expensiveto ship.

FIGS. 1A and 1B are cross-sectional views of an exhaust duct for anattritable engine in a nested and an expanded state, respectively. FIGS.1A and 1B will be discussed together. FIGS. 1A and 1B show attritableengine 100 including combustor section 102, exhaust duct section 104,combustor section housing 106, combustor 108, spring 110, nested exhaustduct 112, outer exhaust duct 114, key 116, and keyway 118.

Combustor section 102 of attritable engine 100 circumferentiallysurrounds exhaust duct section 104, and includes combustor sectionhousing 106 that encases spaced apart combustors 108. Exhaust ductsection 104 includes spring 110 attached to nested exhaust duct 112. Asdepicted in FIG. 1A, spring 110 is in an uncompressed state and can beseen through a phantom line drawing of nested exhaust duct 112. Key 116is attached to outer exhaust duct 114 and can also be seen throughphantom line drawing of nested exhaust duct 112. Keyway 118 is part ofand lies on the external surface of nested exhaust duct 112 and, assuch, is also shown as a phantom line drawing.

Operationally, after the build process is complete, nested exhaust duct112 is extended axially away from combustor section housing 106. Spring110 is compressed as nested exhaust duct 112 is extended until key 116of outer exhaust duct 114 enters and contacts the bottom of keyway 118of nested exhaust duct 112 such that nested exhaust duct 112 does notextend further. Nested exhaust duct 112 is rotated relative to outerexhaust duct 114 and key 116 travels circumferentially around andthrough keyway 118 until nested exhaust duct 112 does not rotatefurther. Compressed spring 110 is allowed to push nested exhaust duct112 axially toward combustor section housing 106 until key 116 of outerexhaust duct 114 is engaged and firmly seated within keyway 118 ofnested exhaust duct 112.

In one embodiment, the total axial length of attritable engine 100 is 11inches (27.9 cm) in the nested state and 21 inches (53.3 cm) in anextended state. In other embodiments, the total axial length ofattritable engine 100 is from 8 inches (20.3 cm) to 14 inches (35.6 cm),inclusive in the nested state and from 18 inches (45.7 cm) to 24 inches(61 cm), inclusive in an extended state. In other embodiments, the totalaxial length of attritable engine 100 is less than 8 inches (20.3 cm) inthe nested state and less than 18 inches (45.7 cm) in an extended state.In other embodiments, the total axial length of attritable engine 100 ismore than 14 inches (35.6 cm) in the nested state and more than 24inches (61 cm) in an extended state.

As depicted in FIG. 1B, spring 110 is in a compressed state and nestedexhaust duct 112 (drawn in phantom) is in an axially extended state. Key116 of outer exhaust duct 114 is engaged in keyway 118 of nested exhaustduct 112. Compressed spring 110 helps to keep key 116 engaged in keyway118 throughout the operation of attritable engine 100, which mayexperience various forces under load such as, for example, vibrational,thermal, and shock.

Attritable engine 100 including exhaust duct section 104 can beadditively manufactured using any metal or alloy that can tolerate thehigh temperature and pressure environment of a gas turbine engine forthe expected useable life of the vehicle, such as, for example, Inconel®625 or other nickel alloys including alloys of nickel, chromium, andiron. However, guided munitions, missiles, and decoys are designed assingle use vehicles and can have a maximum useable life of 10 hours.Heat protection that extends the useable life of the vehicle beyond 10hours can unnecessarily add labor and expense to the manufacturing ofsuch an engine. On the other hand, some UAVs can be designed to performmultiple missions and more heat protection may be desirable. A specificmetal or alloy with or without additional treatments to provide heatprotection can be chosen with such considerations in mind. For example,a thermal barrier layer or coating can be applied to the metal or alloyto extend the useful life of the attritable engine.

FIGS. 2A and 2B are perspective views of the inner section of theexhaust duct showing springs in an uncompressed and a compressed state,respectively. FIGS. 2A and 2B will be discussed together. FIGS. 2A and2B show spring 110, nested exhaust duct 112, keyway 118, and nested lip120. Nested exhaust duct 112 includes spring 110 and keyway 114. Nestedexhaust duct 112 sits inside of outer exhaust duct during themanufacturing process.

Spring 110 is attached to nested lip 120 and is circumferentiallyconformal with nested exhaust duct 112. As depicted in FIG. 2A, spring110 is in an uncompressed state during the manufacturing process. Asdepicted in FIG. 2B, spring 110 is in a compressed state duringoperation of attritable engine 100. Spring 110 is able to slide alongnested exhaust duct 112, but remains circumferentially conformal withnested exhaust duct 112 and remains attached to nested lip 120.

Keyway 118 of nested exhaust duct 112 extends through nested lip 120.Although keyway 118 is depicted in FIGS. 2A and 2B as having a shapesimilar to the letter j, keyway 118 can have any shape that allows a keyto travel through nested lip 120 and, with the help of compressed spring110, retain the key in an engaged state within keyway 118 duringoperation of attritable engine 100.

FIG. 3A is a perspective view of one embodiment of the spring. FIG. 3Ashows spring 210 including rods 211 and angular joints 213. Rods 211provide structure to spring 210 and ensure conformability of spring 210with a nested exhaust duct. On the one hand, angular joints 213 providean elongated structure to spring 210 when in an uncompressed state. Onthe other hand, angular joints 213 provide a shortened structure tospring 210 when in a compressed state and provide a compressive force toretain a key in a keyway during operation of an attritable engine.

FIG. 3B is a perspective view of one embodiment of the spring. FIG. 3Bshows spring 310 including rods 311 and angular joints 313A and 313B.Rods 311 provide structure to spring 310 and ensure conformability ofspring 310 with a nested exhaust duct. On the one hand, angular joints313A and 313B provide an elongated structure to spring 310 when in anuncompressed state. On the other hand, angular joints 313A and 313Bprovide a shortened structure to spring 310 when in a compressed stateand, as such, provide a compressive force to retain a key in a keywayduring operation of an attritable engine.

In one embodiment, springs 110, 210, and 310 can have a radial widthfrom 0.01 inches (0.25 mm) to 0.05 inches (1.27 mm), inclusive. In otherembodiments, springs 110, 210, and 310 can have a radial width largerthan 0.05 inches (1.27 mm). The springs can have many differentgeometries and configurations. Some of the factors considered whendesigning the springs include, but are not limited to, the size of theengine, the compressive force necessary to retain the nested exhaustduct in an extended state during operation of the engine, the dimensionsrequired to withstand the compressive forces such that the springs donot break, the radial distance between the nested exhaust duct and theouter exhaust duct, the ability of the springs to be compressed andslide within the radial distance between the nested exhaust duct and theouter exhaust duct, and other forces experienced during operation of theengine such as, vibrations and thermal stress.

FIG. 4A is a perspective view of the nested exhaust duct including theuncompressed spring. The description and parts of FIG. 4A is the same asthat of FIG. 2A. FIG. 4B is a perspective view of the outer exhaust ductincluding the key. FIG. 4B shows outer exhaust duct 114 including key116 and arresting face 122. Key 116 is attached to the inner surface ofouter exhaust duct 114. Although key 116 is depicted as having apentagon shape in FIG. 4B, key 116 can be any size or shape which allowsthe nested exhaust to be axially extended and retained within a keyway,with the help of the compressed spring, during operation of anattritable engine. Arresting face 122 has a smaller inner diameter thanthe rest of outer exhaust duct 114 and provides a surface for a springto contact and be compressed as nested exhaust duct is extended in anaxial direction. Arresting face 122 also provides a surface, againstwhich, a compressed spring can generate a compressive force to retainkey 116 in a keyway during operation of an attritable engine.

FIG. 4C is a perspective view of the expanded exhaust duct positioned inan extended state inside the outer exhaust duct. FIG. 4C shows exhaustduct section 104 including spring 110, nested exhaust duct 112, outerexhaust duct 114, key 116, keyway 118, and nested lip 120. Outer exhaustduct 114 is depicted with phantom lines. Nested exhaust duct 112 is inan extended state.

Spring 110 is in a compressed state and is attached to nested lip 120and in contact with arresting face 122 (shown in FIG. 5). Spring 110provides a compressive force against arresting face 122 to retain key116 in keyway 118 during operation of an attritable engine. Spring 110does not completely circumscribe nested exhaust duct 112. At least a gaplarge enough to allow key 116 to slide into keyway 118 withoutcontacting spring 110 is present. More than one spring can be present,which provides not only an unobstructed path for key 116 to travel, butalso can provide a way to simply engineer an even weight and compressiveforce distribution around nested exhaust duct 112. Non-symmetricalalignment of the nested exhaust duct within the outer exhaust duct maycause the attritable engine to run less efficiently or fail prematurely.

FIG. 5 is a cross-sectional view of the nested exhaust duct in anextended state including the compressed spring. FIG. 5 shows attritableengine 100 including combustor section housing 106, combustor 108,spring 110, nested exhaust duct 112, outer exhaust duct 114, nested lip120, and arresting face 122. Combustor section housing 106 encasesspaced apart combustors 108, which circumscribes spaced apart outerexhaust duct 114. Nested exhaust duct 112 resides inside outer exhaustduct 114. As depicted in FIG. 5, nested exhaust duct 112 is in anextended configuration and spring 110 is in a compressed state. Spring110 is attached to nested lip 120 of nested exhaust duct 112 and is incontact with arresting face 122 of outer exhaust duct 114.

Both nested lip 120 and arresting face 122 extend in opposite radialdirections from nested exhaust duct and outer exhaust duct, respectivelyand come in close contact with the other opposing exhaust duct surface.In other words, nested lip 120 comes in close contact with the innersurface of outer exhaust duct 114 and arresting face 122 comes in closecontact with the outer surface of nested exhaust duct 112 and preventskey 116 from disengaging from keyway 118 during operation of attritableengine 100. However, nested lip 120 and arresting face 122 are not soclose as to prevent nested exhaust duct 112 to be extended in an axialdirection and rotated relative to outer exhaust duct 114. In oneembodiment, nested lip 120 and arresting face 122 extend a distance fromnested exhaust duct and outer exhaust duct, respectively, from 0.1inches (2.54 mm) to 0.25 inches (6.35 mm), inclusive.

An exhaust duct with multiple nested exhaust ducts is also contemplated,herein. Each additional nested exhaust duct would have a key on itsinner surface and a keyway on its external surface and a spring to helplock each section in place. Such a system can be described as havingtelescoping capabilities.

Using additive manufacturing techniques, an attritable engine can bebuilt with an integrally extendable exhaust duct, which can be assembledinto place without any secondary operations. The nested exhaust duct ispulled axially away from the inlet side of the unitized body and islocked into place after the build process is complete. Building theattritable engine with an integrally extendable exhaust duct decouplesthe axial length of the design build from the size of the build chamber.Reducing the axial length of the attritable engine during manufacture,decreases the overall build time and the size of the build chamber,reducing costs. Furthermore, the attritable engine prior to extendingthe exhaust duct has a smaller footprint and, as such, is easier andless expensive to ship. The exhaust duct in an extended configuration isalso more prone to damage such as, for example, dents, during handlingand shipping.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

An exhaust duct for an engine includes an outer exhaust duct and anested exhaust duct capable of having at least two configurations. Thenested exhaust duct is circumferentially surrounded by the outer exhaustduct for a first length of the nested exhaust duct in a firstconfiguration. The nested exhaust duct is circumferentially surroundedby the outer exhaust duct for a second length of the nested exhaust ductin a second configuration, which is less than the first length.

The exhaust duct of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

The exhaust duct includes an integrally formed key on an interiorsurface of the outer exhaust duct.

The exhaust duct includes an integrally formed keyway on an exteriorsurface of the nested exhaust duct.

The integrally formed key is located away from the integrally formedkeyway in the first configuration and wherein the integrally formed keyis located within the integrally formed keyway in the secondconfiguration.

The exhaust duct includes an integrally formed nested lip on an exteriorsurface of the nested exhaust duct.

The exhaust duct includes a spring attached to the nested lip andcircumferentially conformal with the nested exhaust duct.

The spring is uncompressed in the first configuration and the spring iscompressed in the second configuration.

The compressed spring is configured to exert a compressive force inorder to retain the key within the keyway during operation of theengine.

The exhaust duct includes an integrally formed arresting face on aninterior surface of the outer exhaust duct.

The integrally formed arresting face is located away from the spring inthe first configuration and the integrally formed arresting face is incontact with the spring in the second configuration.

The first length is substantially equal to the axial length of thenested exhaust duct.

A method of manufacturing an axially extendable exhaust duct for anengine includes manufacturing an outer exhaust duct and a nested exhaustduct capable of having at least two configurations. The nested exhaustduct is circumferentially surrounded by the outer exhaust duct for afirst length of the nested exhaust duct in a first configuration. Thenested exhaust duct is circumferentially surrounded by the outer exhaustduct for a second length of the nested exhaust duct in a secondconfiguration, which is less than the first length.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

The method includes manufacturing an integrally formed key on aninterior surface of the outer exhaust duct and an integrally formedkeyway on an exterior surface of the nested exhaust duct.

The integrally formed key is located away from the integrally formedkeyway in the first configuration and the integrally formed key islocated within the integrally formed keyway in the second configuration.

The method includes manufacturing an integrally formed nested lip on anexterior surface of the nested exhaust duct, a spring attached to thenested lip and circumferentially conformal with the nested exhaust duct,and an integrally formed arresting face on an interior surface of theouter exhaust duct.

The spring is uncompressed and the integrally formed arresting face islocated away from the spring in the first configuration and the springis compressed and the integrally formed arresting face is in contactwith the spring in the second configuration.

The compressed spring is configured to exert a compressive force inorder to retain the key within the keyway during operation of theengine.

The method includes extending the nested exhaust duct in a firstconfiguration in an axial direction, rotating the nested exhaust ductrelative to the outer exhaust duct, and allowing the spring to exert acompressive force to retain the key within the keyway.

Manufacturing is performed using additive manufacturing techniques.

An axially extendable exhaust duct for an engine includes an outerexhaust duct having an integrally formed key on an interior surface ofthe outer exhaust duct and a nested exhaust duct with an integrallyformed keyway on an exterior surface of the nested exhaust duct, whichis capable of having at least two configurations. The nested exhaustduct is circumferentially surrounded by the outer exhaust duct for afirst length of the nested exhaust duct in a first configuration and thenested exhaust duct is circumferentially surrounded by the outer exhaustduct for a second length of the nested exhaust duct in a secondconfiguration, which is less than the first length. The exhaust ductalso includes a spring attached to and circumferentially conformal withthe nested exhaust duct. The spring is uncompressed in the firstconfiguration and the spring is compressed in the second configurationand configured to exert a compressive force in order to retain the keywithin the keyway during operation of the engine.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. An exhaust duct for an engine, the exhaust duct comprising: an outerexhaust duct; and a nested exhaust duct capable of having at least twoconfigurations, wherein the nested exhaust duct is circumferentiallysurrounded by the outer exhaust duct for a first length of the nestedexhaust duct in a first configuration and wherein the nested exhaustduct is circumferentially surrounded by the outer exhaust duct for asecond length of the nested exhaust duct in a second configuration,which is less than the first length.
 2. The exhaust duct of claim 1 andfurther comprising an integrally formed key on an interior surface ofthe outer exhaust duct.
 3. The exhaust duct of claim 2 and furthercomprising an integrally formed keyway on an exterior surface of thenested exhaust duct.
 4. The exhaust duct of claim 3, wherein theintegrally formed key is located away from the integrally formed keywayin the first configuration and wherein the integrally formed key islocated within the integrally formed keyway in the second configuration.5. The exhaust duct of claim 4 and further comprising an integrallyformed nested lip on an exterior surface of the nested exhaust duct. 6.The exhaust duct of claim 5 and further comprising a spring attached tothe nested lip and circumferentially conformal with the nested exhaustduct.
 7. The exhaust duct of claim 6, wherein the spring is uncompressedin the first configuration and wherein the spring is compressed in thesecond configuration.
 8. The exhaust duct of claim 7, wherein thecompressed spring is configured to exert a compressive force in order toretain the key within the keyway during operation of the engine.
 9. Theexhaust duct of claim 8 and further comprising an integrally formedarresting face on an interior surface of the outer exhaust duct.
 10. Theexhaust duct of claim 9, wherein the integrally formed arresting face islocated away from the spring in the first configuration and wherein theintegrally formed arresting face is in contact with the spring in thesecond configuration.
 11. The exhaust duct of claim 1, wherein the firstlength is substantially equal to the axial length of the nested exhaustduct.
 12. A method of manufacturing an axially extendable exhaust ductfor an engine, the method comprising: manufacturing an outer exhaustduct; and manufacturing a nested exhaust duct capable of having at leasttwo configurations, wherein the nested exhaust duct is circumferentiallysurrounded by the outer exhaust duct for a first length of the nestedexhaust duct in a first configuration and wherein the nested exhaustduct is circumferentially surrounded by the outer exhaust duct for asecond length of the nested exhaust duct in a second configuration,which is less than the first length.
 13. The method of claim 12 andfurther comprising manufacturing an integrally formed key on an interiorsurface of the outer exhaust duct and an integrally formed keyway on anexterior surface of the nested exhaust duct.
 14. The method of claim 13,wherein the integrally formed key is located away from the integrallyformed keyway in the first configuration and wherein the integrallyformed key is located within the integrally formed keyway in the secondconfiguration.
 15. The method of claim 14 and further comprisingmanufacturing an integrally formed nested lip on an exterior surface ofthe nested exhaust duct, a spring attached to the nested lip andcircumferentially conformal with the nested exhaust duct, and anintegrally formed arresting face on an interior surface of the outerexhaust duct.
 16. The method of claim 15, wherein the spring isuncompressed and the integrally formed arresting face is located awayfrom the spring in the first configuration and wherein the spring iscompressed and the integrally formed arresting face is in contact withthe spring in the second configuration.
 17. The method of claim 16,wherein the compressed spring is configured to exert a compressive forcein order to retain the key within the keyway during operation of theengine.
 18. The method of claim 17 and further comprising: extending thenested exhaust duct in a first configuration in an axial direction;rotating the nested exhaust duct relative to the outer exhaust duct; andallowing the spring to exert a compressive force to retain the keywithin the keyway.
 19. The method of claim 12, wherein manufacturing isperformed using additive manufacturing techniques.
 20. An axiallyextendable exhaust duct for an engine, the exhaust duct comprising: anouter exhaust duct having an integrally formed key on an interiorsurface of the outer exhaust duct; a nested exhaust duct with anintegrally formed keyway on an exterior surface of the nested exhaustduct, which is capable of having at least two configurations, whereinthe nested exhaust duct is circumferentially surrounded by the outerexhaust duct for a first length of the nested exhaust duct in a firstconfiguration and wherein the nested exhaust duct is circumferentiallysurrounded by the outer exhaust duct for a second length of the nestedexhaust duct in a second configuration, which is less than the firstlength; and a spring attached to and circumferentially conformal withthe nested exhaust duct, wherein the spring is uncompressed in the firstconfiguration and wherein the spring is compressed in the secondconfiguration and configured to exert a compressive force in order toretain the key within the keyway during operation of the engine.